Porous V(2)O(5)/RGO/CNT hierarchical architecture as a cathode material: Emphasis on the contribution of surface lithium storage

A three dimensional vanadium pentoxide/reduced graphene oxide/carbon nanotube (3D V(2)O(5)/RGO/CNT) composite is synthesized by microwave-assisted hydrothermal method. The combination of 2D RGO and 1D CNT establishes continuous 3D conductive network, and most notably, the 1D CNT is designed to form hierarchically porous structure by penetrating into V(2)O(5) microsphere assembly constituted of numerous V(2)O(5) nanoparticles. The highly porous V(2)O(5) microsphere enhances electrolyte contact and shortens Li(+) diffusion path as a consequence of its developed surface area and mesoporosity. The successive phase transformations of 3D V(2)O(5)/RGO/CNT from α-phase to ε-, δ-, γ-, and ω-phase and its structural reversibility upon Li(+) intercalation/de-intercalation are investigated by in situ XRD analysis, and the electronic and local structure reversibility around vanadium atom in 3D V(2)O(5)/RGO/CNT is observed by in situ XANES analysis. The 3D V(2)O(5)/RGO/CNT achieves a high capacity of 220 mAh g(−1) at 1 C after 80 cycles and an excellent rate capability of 100 mAh g(−1) even at a considerably high rate of 20 C. The porous 3D V(2)O(5)/RGO/CNT structure not only provides facile Li(+) diffusion into bulk but contributes to surface Li(+) storage as well, which enables the design of 3D V(2)O(5)/RGO/CNT composite to become a promising cathode architecture for high performance LIBs.